Last Updated: May 1, 2024
Krill
The term Krill is derived from the Norwegian description for “young fry of fish”. Krill are marine crustaceans that belong to the order Euphausiacea. Although there are many species of Krill only Antarctic Krill (Euphausia superba) and Pacific Krill (Euphausia pacifica) have been harvested for human consumption. Krill look like tiny shrimp and weigh less than 2 grams and are 6–8 millimeters in length. Krill are found in large swarms that may contain as many as 1 million animals in each cubic meter of seawater. This dense population of swarms make Krill an ideal species for harvesting. In fact, it is this clustering of Krill that make them ideal food for whales, seals, and sea birds.
Krill have an extremely high nutrient composition which makes them ideal for human consumption. The dietary benefits of Krill are many as they are low in caloric content relative to nutritional composition. Krill are composed of approximately 1%–4% total lipid and 12%–16% total protein per unit wet weight. On a dry weight basis the total lipid content rises to from 12%–50%. Factors that affect the lipid content of Krill preparations include the season of capture, age, and the lag time between capture and freezing. Among the lipids found in Krill are the essential fatty acids α-linolenic (ALA) an omega-3 polyunsaturated fatty acid (PUFA) and linoleic (LA). Krill is low in overall saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) content but high (approaching 50% of total lipid concentration) in PUFA.
Composition of Krill Oils
The advantage of Krill oil is that the composition of the PUFAs found in the oil is primarily omega-3 fatty acids. In fact oils extracted from Antarctic Krill harvested in the winter contain approximately 20% omega-3 PUFAs. Of clinical significance to humans is that the omega-3 PUFAs found in Krill oil are predominantly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). For more information on the clinical benefits of EPA and DHA see the Omega-3 & Omega-6 Fatty Acid Synthesis, Metabolism, Functions page, the Eicosanoid Metabolism: Prostaglandins, Thromboxanes, Leukotrienes, and Lipoxins page, and the Bioactive Lipid Mediators of Inflammation page.
In addition to an abundance of EPA and DHA in Krill oils there is a high content of several lipid soluble antioxidants. Of particular significance is the presence of the antioxidant astaxanthin. For more information on antioxidants such as astaxanthin go to the Plant-Derived Phytochemicals and Antioxidants page. The deep red color of Krill, as well as many other crustaceans, is due to the presence of astaxanthin.
Fish oils are also enriched in EPA and DHA accounting for the known clinical benefits to the consumption of a diet high in fish or for the taking of fish oil supplements. However, whereas the majority of EPA and DHA in fish oils are found in triglycerides (TG; also termed triacylglycerides, TAG), in Krill oils these PUFA are found predominantly in phospholipids (PL).
Why this is potentially of clinical significance is related to the absorption and tissue distribution of lipids derived from dietary triglycerides versus phospholipids. Upon consumption triglycerides are acted upon by pancreatic lipase yielding two molecules of free fatty acid (FFA) and a 2-monoglyceride (2-MG). Both the 2-MG and the FFA are then absorbed by the enterocytes of the intestine.
On the other hand dietary phospholipids are acted upon by pancreatic phospholipase A2 (PLA2) yielding a FFA and a lysophospholipid (lysoPL). The action of various phospholipases can be seen in the Synthesis of Fatty Acid, Triglycerides, and Phospholipids page as well as in the Signal Transduction Pathways: Phospholipids page.
Following uptake by the intestinal enterocytes the lipids are re-esterified forming triglycerides and/or phospholipids. In the animal kingdom there is a preference for the esterification of the sn-2 position with an unsaturated fatty acid. Thus, because the action of PLA2 removes the fatty acid from the sn-2 position of phospholipids, when they are re-assembled in the intestine there is a preference for the incorporation of an unsaturated fatty acid. Since Krill oils are enriched in the PUFA, EPA and DHA, consumption of Krill oils results in the absorption and distribution of a high proportion of EPA and DHA containing phospholipids. Phospholipids are enriched in the membranes of all cell types and in this capacity play important roles in cell membrane integrity and functions such as signal transduction and inflammatory process regulation.
Of significance to the source of omega-3 PUFA it has been shown that the absorption and distribution of EPA and DHA derived from dietary phospholipids is higher when compared to dietary triglycerides. This is in part due to the fact that DHA derived from dietary triglycerides is found at a higher concentration in the feces (i.e. wasted) compared to that derived from phospholipids.
Nutritional Benefits of Krill Oil Consumption
Numerous clinical benefits have been ascribed to the consumption of diets high in omega-3 PUFA. Because fish oils harbor EPA and DHA primarily in the form of triglycerides, whereas Krill oils contain these fats in phospholipids, and given the higher efficiency of absorption and tissue distribution of EPA and DHA derived from phospholipids, it is suggested that consumption of Krill or Krill oils will have higher clinical significance compared to fish or fish oils. Whereas the clinical literature is ripe with the benefits of fish oil, the clinical benefits of Krill and Krill oil consumption are only just emerging. Many of the benefits of Krill oil overlap those of fish oils, i.e. prevention and/or treatment of inflammatory and neurological disorders, and prevention and reversal of insulin resistance. The presence of astaxanthin is thought to be the responsible agent for the observed anti-inflammatory, analgesic, and hypolipidemic effects of Krill oil.
In a well controlled double-blind clinical trial, high dose Krill oil consumption was shown to result in a significant reduction (25%) in circulating triglycerides in male and female subjects exhibiting mild to high serum cholesterol and triglyceride levels. In addition to reductions in triglyceride levels the treated patients exhibited reductions in cholesterol levels following Krill oil consumption. Of significance in this study was the fact that Krill oil consumption led to a reduction in LDL of up to 39% and an increase in HDL of up to 60%. These effects of Krill oil are significant since a comparison with the effects of fish oil consumption in the same study showed that there was no effect of fish oil consumption of the level of LDL. Although the results of this study are intriguing the subject size was small and there were no adjustments made for other influencing factors such as diet, gender, genetics, and smoking. Therefore, further studies on the cardiovascular benefits of Krill oil consumption are needed.
In laboratory animals fed a high fat diet, the addition of Krill oil supplementation has been shown to reduce the incidence of hypercholesterolemia and to reduce hepatic steatosis (fatty liver syndrome caused by increased fat storage) which in turn reduced the potential for hepatomegaly. Krill supplementation in these animals also led to significant reductions in fasting plasma glucose levels and increased the serum concentration of the adipose tissue hormone, adiponectin. These effects indicate that human consumption of Krill oil could lead to reduced development of type 2 diabetes or to at least aid in the reduction of hyperlipidemia and hyperglycemia in these patients.
Although many of the cholesterol and glucose lowering effects of Krill oil can be attributed to the presence of EPA– and DHA–containing phospholipids, it should pointed out that the presence of astaxanthin may have a significant role. Astaxanthin administration to spontaneously hypertensive rats has been shown to result in increased plasma adiponectin, reduced plasma glucose levels, and increased insulin sensitivity. In addition, obese mice fed astaxanthin resulted in reduced liver weight, reduced liver triglycerides, and reduced plasma triglyceride levels.
The anti-inflammatory action of Krill oil suggests that its consumption may be beneficial for the treatment of auto-immune disorders such as rheumatoid arthritis (RA). In a recent study using an in vivo model of rheumatoid arthritis in mice, the effects of Krill oil supplementation were assessed on several parameters including histopathology and analysis of the levels of several immunomodulating cytokines. These experiments are performed by injection of collagen into the joints of the hind paw which results in an arthritis reaction in the joint in 3–4 weeks. In the mice fed Krill oil there was a significant reduction in the infiltration of inflammatory cells into arthritic joints and a reduction in synovial layer hyperplasia compared to untreated control animals. In addition the level of histopathology was significantly reduced. The results from this study suggest that human consumption of Krill oil may be a useful intervention in the treatment of the clinical signs of inflammatory arthritis.
The omega-3 fatty acids DHA and EPA have also been shown to be important for normal brain development and function. Several studies have demonstrated that DHA is essential for proper development of the prenatal and postnatal central nervous system. The benefits of EPA appear to be in its effects on behavior and mood. In clinical studies with DHA and EPA there has been good data demonstrating benefit in treating attention deficit hyperactivity disorder (ADHD), autism, dyspraxia (motor skills disorder), dyslexia, and aggression.
In patients with affective disorders consumption of DHA and EPA has confirmed benefits in major depressive disorder and bipolar disorder. In addition, some studies have demonstrated promising results in treatment of schizophrenia with some minor benefits in patients with borderline personality disorder. Of significance to these effects of EPA and DHA on cognition, mood and behavior is the fact that administration of omega-3 fatty acid containing phospholipids (such as those present in Krill oils) are significantly better than omega-3 containing triglycerides such as those that predominate in fish oils.
The effects of Krill oil in the management of premenstrual syndrome (PMS) has also been investigated. The results of one double-blind controlled study demonstrated that women taking Krill oil supplements reported fewer symptoms of PMS such as breast tenderness, bloating, joint pain and swelling compared to women taking fish oil supplements. The women taking the Krill oil also took less pain medication. When assessing the effect of Krill oil consumption on the emotional effects of PMS, women reported that they experienced fewer and/or less intense feelings of stress, anxiety, depression, and irritability. It is suspected that the reduced emotional distress in these women was due to the influence of DHA on brain function, a well known effect of this PUFA.